Aerial navigation



,NV' 14, 1950 H. cHlRl-:lx 2,530,287

AERIAL NAVIGATION Filed April 17, 1947 3 Sheets-Sheet 1 Nov. 14, 1950 H CHIREIX 2,530,287

AERIAL NAVIGATION Filed April 17, 1947 5 Sheets-Sheet 5 @genis patented Nov. 14, 1950 AERIALV NAVIGATION Henri-Chirei-x, Paris, France, assignor to Societe' Francaise Radio. Electrique, a corporation.. of"

France Application Aprilil'zg'l947, Serial No. 742,086

In France May 5, 1944.

Section 1, Public Law 690, August 8,1946y Patent expires May15", 1964 8 .Claims The. present invention is especially,l but notexelusively, Aapplicable; to1 aerial navigation Its.

chief-object. is to'obta-in. onboard, a mobile craft, and-particularly anfaircrait, on the screen oiai cathode ray oscillograph, ,and intheA most improvedV aspect. of the; invention, not only. the

simultaneous indication ofthe directionof radio. -beaeons installed on the.. ground, but also the distance of said .beacons fromthe-aircraft.- It. is,-

in fact, proposedy tov obtain* onsaid screen, an image suchas that shovvnin Figure 1, the length of thefhalfflinesZ OA, OB., QG ,indicating vthe dis.-

ta-nce from, theaircraft.- to the transm-i-tters.,-A,

B, AC.. locatedon theg-round, the `direction ofv the haii-.lines directly givingthe-true bearing of the aircraft with respect to. said transmitters.

' Anessential; characteristic of the .invention isvr that on .boardthe aircraftL the reception. of all. the necessary; inio-rmationfrom which mayf be,- obtainedthe-true. bearing, of, the transmitters;-

A,, B,C, etc.v can be effected by means of a.- single effect.- in thehorizontal. plane.

radio beacons installed on. the ground. The in.- stallation on board the. aircraft .is thus consider-- ably simplified, and the errors, Whichmight-be. caused by the-- directive-,reception on board. the

aircraft of Very --short Wailea-of Awhich `the .use is contemplated, are eliminated-and alsothe-neces.- sityof combining the indications obtained. byv goniometry .with .the` radioFeornpass, in :order to,

determi-ne.. the true bearing.

The invention Willbe better-understood from.

the-description below given of someembodimentsaof' theinvention. takenA in connection.y withA the accompanying .drawings wherein:

Figure l shows an indication on the screen of" a cathode ray tubeas-obtainedin .the-operation of the .-in-vention;

Figui-e 4-2. show-s schematicallyy the distributionot-theradio beacons in a territory being served; Figuresv :3a t and .3b show a non-limitative: ex.-

amplerofa1, scheme of f a-..rad-io:-. beacon according toy fthe.- invention;

Fig-ure 4 shows.. a. circuit. diagramof: an nonlimitativeexample. of a freceiver;aecordingto. the-r invention;

Figure shows;y two. variants. of g. thel signals utilized.; i

Figure-62 shows anotherfindieationontnescreen:

otray cathode raytube;.;and v Figures 7 and 8 show simplified diagrams-of:

modications.ofrthereceirers;V

TheY arrangementaccording to the invention. will rstbe described inthe case in which it is proposed to obtain-on board the aircraft," the simultaneousY indication of" the directionY ofthe radio beacons onfthel groundwithont indication oft-the distance, and a"'description'will thenbe given of the addtionalinstallations to be made in the-.case inwhich itis .desired to add the. in. dicationof the distances.

In the first case contemplated, the installation on board the aircraftis-.redncedto a receiver associated with .the vaerialand .to a .cathode ray,.- oscillographassociated Witnthe receiver. In the... second. case, the -installation on board. should ...be completedv by a transmitter.. transmitting` short.. impulses.

The ground' installation comprises, accordingYV to Figure 2,v special/radio beacons, the operation.. 0f which will be described, and all of which operate onzthe-fsamefwavelength, preferably on short waves. Said radio. beacons are, for; inestance, locatedatan average distanceoi 150. kilometres.. from one. another. However, they donot.all. transmit..simultaneously; for instance. only theradio. beacons-designated by l, transmit.. simultaneously, thengthose designated by Land. so forth,v up tdthose designated by 9,- then, start-y ing again by those designated by. le This. resultr can be obtained, for example, in the following ,Wayl

All the transmitters .of-.the territory; operating: on .the same wavelength arezsuppl-ied with power: from a three-phase -cycle-supply-system. or inter-connected supply systems. The..control de.

,S vice for the transmission is connected to a synchronous.-Y distributor.. In this manner; caen; radiobeacon is set inaction;ior instance --50H times per second'for periodsof lm of- .a seco-nd.;V These. radiobeaconsare, turtl'ierniore,v keyedn at a. slower. cadence. .soY as to transmit ay call. sign.v which. characterisesthem. By means. of.' this areY rangement errors.- ot bearing, which might-.be caused. by; the: simultaneous.: reception of:- several radio beacons operating. on, thesamezwayeleng-tm, are avoided.

The construction of one of Vthese radiol beacons, all of whichare.- `Wil-l-r-ioW-loe described.. A l radiol beacon. @Figureei comprisesirr reality three; transmittersfoperating-1 onv vsz-avelengtlns.;`

Y. which. are Very; close; together; ,n corresponding;

to the-frequency w.1 .iarcorrespondingatd the fre-e quency;` wa: corresponding tethe vfrequencyves...v Said transmitters are all modulated: atV the:- same frequency Thezrst .of saidtransmitters u (Figure- 3.).1

two output terminals and supplies, through a feeder, on the wavelength M, the vertical aerial I. The maximum amplitude of the current owing through said aerial is expressed by:

K being the percentage of the modulation. At a given distance, d, from said aerial the electric field which it produces is of the form:

(l) E1 cos witll-I-K cos Qt] conditionally on changing the time origin so as to take into account the time of propagation corresponding to this distance.

The second of said transmitters is separated from the third by suitable insulating devices and has three pairs of output terminals; the first pair of terminals supplies, in phase opposition, the aerials a and b of an aerial system II of the Adcock i'lxed type, the second pair of terminals supplies, in phase opposition, the aerials c and d of this same aerial system II. The four aerials, a, b, c, d, are arranged along the edges of a square base prism having a length of side which is small compared tothe wavelength. The iirst of the pairs l of output terminals supplies a voltage of the form.

U1.=U cos @2t sin Qt Whereas the second'pair of terminals supplies a voltage of the form:

Uz=Uo cos wzt cos Slt In other Words, the amplitude of the high frequency signal at frequency wz issinusoidally modulated, at the frequency S2, by two identical modulating groups, the modulations being in quadrature of phase. The electric field of such a system, at the same given distance as hereinbefore, equals:

E cos Wzt (cos (2t cos p-I-sin Qt sin go) the time t being reckoned from the same origin as in the Expression l, and the angle q, which is the bea-ring of the place of reception with respect tothe transmitter, being reckoned from the plane containing-the aerials c and d, in the direction of rotation of the field. Finally, the third pair of terminals (Figure 3) injects in the aerial I a current of the form:

Iacos wt i. e. an unmodulated current. It follows that the eld, at the given distance, on the wavelength )(2, can be expressed by: l

(2) E2 COS wzt [l-l-,u COS (QP-92)] in which ,u designates the ratio of the field supplied by the aerial system II on A2, to the eld supplied by the aerial system I likewise on A2.

The third of said transmitters (Figure 3) which supplies the aerial system III and the aerial system I, is in all respects similar to the second, but the supply connections of c, d are reversed in III relatively to what they were in II, so as to obtain, at the given distance, a iield of the form:

(3) E3.cos wat [1 /i cos (Slt-M0] The voltages induced in the aerial by the various elds (i), (2), (3) are fed to the high frequency portionv II of a receiver where they are amplied together and optionally subjected to change of frequency; the three waves corresponding to M, )(2, )s are then separated in lters I2 and then separately detected by the detectors I3.

Conditionally on the times of transmission being the same for the three adjacent wavelengths, a condition which can be readily obtained, in view of the three contiguous waves to be received having xed frequencies, three detected voltages are obtained which are of the form:

(4) B cos Qt for )(1 (5) A Cosmi-(p) for )(2 (6) -A Cosmi-Hp) for M p being the bearing with respect to the radio beacon considered. By means of these three voltages, it is possible to operate the cathode ray oscillograph I4, of which only the deecting plates for the beam have been shown, and the control of luminosity by acting on the Wehnelt cathodehas been indicated by an arrow f.

The detected voltages )(2 and M. are fed to two limiters formed by two pentodes I5 whose outputs are connected to circuits I6 tuned to the pulsation Il. For this purpose, a resistance, p of high value, relative to the corresponding gridcathode resistance, is inserted in the grid circuit. From the voltages produced in the circuits I6, there is created, in each of the groups coupled to the circuits I0, two equal voltages in phase opposition, one obtained by coupling an untuned circuit I?, the other a tuned circuit I8, these two voltages being combined as shown in Figure 4. Without any other contrivance, therefore, when the bearing varies, a diametrical line would be obtained which would rotate 360 when the angle qa varies from 0 to 180, and there would be an ambiguity of 180.

On the other hand, by controlling the Wehnelt cathode by means of the voltage -cos Qt transmitted by M, the cathode ray can be extinguished over a half diameter, since whatever be the value of rp, the radial deflection of the spot is in phase with -cos Slt.

It will be immediately understood that by way of a variant, it is possible, instead of emitting always on the wave length )(1 during 1/450 second, not to emit on this wave length except during comparatively short impulses transmitted at the frequency F and having their axes as shown in Figure 5. As said impulses control the illumination of the Wehnelt cathode of the oscillograph, only the end of the half-diameter will be illuminated, so that the diagram will nally be that of Figure 6.

In View of the fact that owing to the arrangements made, geometrically adjacent radio beacons do not transmit simultaneously, the airborne installation will successively give the bearings of the various radio beacons located in the region, and as the bearings of each of them are taken, in the example in question, 50 times per second, there will be produced, owing to the persistence of retinal impressions, the impression of a continuous bearing being given.

The modiiications and additions which have to be made to the installations above described in order to obtain, in addition to the foregoing indications, those of the distances, will now be described.

The airborne installation is completed by the 51 addition/.ef a. Smallimnulse. transmitteralso open-` 7r atme: Qtr-.ishortfwavesfrbut .on .a .1 diiferent .wave-l length.LV Said trans-mitten transmits via-.the anrtelina .on the aircraft short impulses.l of; a; few,- milliseconds durationvfor.rinstaneeaat; a, ,cadenI-iee atftheiaver-t XIQWE:

are; the Operation: .voltea-,ess.whichi are 20,

` generatoreeuel .itezthe time-.taken tetravelzzbyfelee.- y trames?! ,letwaves t0 i andrfrem the` extreme 25, rangefwhieh has. been allotted,tethefinstellatiem Thus, tithe extreme renee is, :15a-kilometres fier-f. instance ,said time isul millisecond.

Thersewetoethfvoltaee is. fed. on: the*one.1r-1aed,y to.: thethieh L frecuentarA portion. of. thereceiyer 30. SQ eetereei-itrel the sensitivity thereof in; the sense; 0f: en increaseef: the sensitivity aefrom the.. transmission Of--an imniilse.Y and. on -thetother handlto-thefrejection'grids of thezpentodes I- 5 which are negativelywloiasedwhen `in tl-ie inoper 35L ative state. There is thus created a limitation threshold of the limiters lsuchl that the limi'- tation value increases linearly with the time as fromlthe transmission of an impulse. It follows that: .theamnlitudefetthefields produced :the 40 oscilloscope/.bythe receipt of; the signals of wavey lengths :les te elsofinerease .linearly ,with1t11e time, and-the same applies tothe radialv deflection.

On. the ground.; the :installation of i each; radio balcon; is completed bythe addition-of; areceiverwhich reeeiyesfthetransmissions/fromme air-V` craft during the pulses transmitted by the synchronous distributor atfiftyfcycles per second, on the Wavelength M, which transmission itself controls the illumination.ofethe.cathode@restitutieLv 50V at-the receiving-end.-

Of course, inthis-case-inwhich the indications` of=;-'distance Y are..o.btainee,v it fismecessarywto give the frequency Q a much higher value thana-inthe l rstcase described. in .\avhich.` it Wasnot contem- 55 platedfto .give.ltheLdistance.:l The frequencyla should'ibe chosenequal to. a fewlhundred;,ki1o-... cycles sotthatftheduration of` theilluminationoflthe screen covers- .at I#least .several cycles .of Vsaid frequency. This-.- involves `a .stricten di-ferentia- 50 tion=of the three AWaves ALM, is; itis nevertheless-1; possibletoeaccommodateall these transmissions soeas only toy cover-an .total `frequencybandofa few--megaoyclies, i-.e. a; frequency band'WlfrichyisV smaller-themen equal tothat ofafnormal telev-i 05 sionstation.P

As regards theoperationat the lreceiving--e1=ld-'; this-.isfefiected asl-follows (Figure eli. Astthe wavelengths`v` A2' and 1 :k3 `are radiated, during 2:2Y milliseconds A Y everyw t 20 milliseconds (independ- 70; ently of the call signor the stationwhichniedri-A lates the transmissionat a'muchslower cadence) ,1- the cathode ray-ef thecathode ray oscillograph 4 islsubjeetedtoetheelds set-up bythe rvoltages produced circuits 46e*- 'furthermorefbytthe Anl amazes? eectfof: thesaw-tooth;:voltages-f ofthe-generator I 9, increase of"amplitude:I vluf-"these eld'sfwith ree spect.. to apredetermined valuer varies linearly? with thedurationoi each tooth of saw-tooth`v wave;v The instants .when this.l saw-tooth cornf-V mences is after the instant-Which correspondstto. the generation-of the pulse. since there inter:- posed adelay linebetween: the' outputofitheeair'- borne transmitter and the timerbase generatorto 1 take accountof' the delay; in' transmission of theI central antennav IA until the-waves leaving.: the? aircraft reach the emit-ting station. Nevertheless, no spot isvisible on the screen so longaas.: the Wehnelt cathode is blocked. This blockage 1Q isremoved `by the signal transmitted by-.the yan.

tenna I of fthe transmitter.l The l'Wehnelt 'cathode will therefore onlyoperatefora. particular` valueof the amplitude of'thelields,which via-.lineel is in direct relationv with thetime passed since;- thetransmission ofthe impulse from-theaircraft, i. e. with the distancev oiithefaircraft from.A theI transmitter. Therefore, in the case in which the pulse provided bythe arcraft'is not released later than the pulse `provided by the beacon, the

vdiagramV of Figure; 1 will?` be obtained.

Itfwill. loe-observed that thev transmission onNv M only=talres place bythe effectof theimpulses-Y received andonly`v during the.itransrnittinevpee riods of the radio beacons. If these transmitting. periodslare asv.in"theexampleschosenf 2.2;.'

seconds-leveren'Ztl-.millisecondsa and ii` the: ini-epulsestransniitted'-iiromthe airorait .reliever oneA another every 12 milliseconds, only:oneimpulseK out f of# 5 `Will#operateethe--rad-io beacon, since when Seidl- 'beacon is inoperative- Thei Wehnelt r cathode lofttheoseil-loeraplfi .Wlilitherefore ber-ile... luininated 16: to lil times per secondi; sincei 1.900/6tl-16l66g which issu-icient tevproduee-,-f owing-to the-persistenceof retinalf impression., ena ha-noedJ-il necessaryhy :the .remanentesoif the fluorescence-o=fvthe-screein1 the impressionfof a` ('ligure-V 61)- or of a-continuousehalfelinee (Figure l).

The caselwilk newbe considered ira-which sevf-f-A eral aircraft v-arefilying over f the .sameeregion. Etf fi pulse-transmitter ori-each aircraft .should not continuous the` navi-gator only-fi-reomringt-:to use'A remainder-of `the-time for v-otlflerpurposes. Itfis .possible, in particulanas`- known, t@ group-'onfsai'd oscil-lographtheindications 'ofi-other -i-1frstruments on boardftheai-rcraftt, such-as -artieiall horizon;I gyrocornpass, air-speed ifri-dicator,v blindeA approach indicator; etc.- t however twoaireziait"A4 Y transmit pulses simultaneouslythereisaoff:

le-risk', stiliilin the easeuofftheexample chosen.` Forv this lp1-ir1avos,e,--it Wil-1t betobservedthat:

The secondfaircrfaf-tf justiii-ke-the Afirst, only, capable offstarting| the trans-missionfcn )l1-A 16'- or vv1-'1 timeseperesecond.lL

2; Fortesfmapivextending over-159'- lsilonietres; A

the AYsavv-toeth1-voltageof the: generatory 123i4 of* Fig-urealastsel` miliisecondand is-repeated about* 33etimesper secondi Duringwmoretthan- 98%1ofT-i theetimef4 theI Oscilloscopesaboardv '=the, trstsatre crsuiteriseblocked:5

atadas?, .i

3; If", however, the two aircraft emit pulses simultaneously in the course of a period ofoperation of the beacon under consideration, the second aircraft, called the jammer illuminates the screen of the oscilloscope of the rst aircraft while the cathode ray beam of the latter oscilloscope executesits diametral sweep; but the luminous marks thus started will have no consistency. In fact, if the cadence of the impulses on the disturbing aircraft is very slightly different from that of the disturbed aircraft (12.0i milliseconds for instance between the impulses instead of l2 milliseconds), which is obviously exact lsynchronisrn, only one impulse out of l would be capable of starting the transmission on M, the second impulse which would start it having a lag of 100 microseconds with-respect to the period. when it should arrive in order to mark the same point on the screen of the osciliograph; it would therefore make a transient mark kilometres further on, and so forth. All these trarsient vmarks, which are distributed haphazard along a line forming an angle p 'with the origin axis, will not in practice hinder the reading since the wanted mark corresponding to the desired bearing will be much more luminous owing to the fact that it is produced by the accumulation, at the same point, of the successive impulses transmitted.

Finally, it is obvious that the disturbance which iscapable of being caused by the jamming aircraft will in no way upset the accuracy of the bearing indicated.

Although the installation according to the invention has just been described in its most complete form (indications of bearing and of distance), it may, the most often, be carried out in the simpler form of an indication of a bearing only. It will be observed, in fact, that if the pairs of -aerials c, d of Figure 3 is for instance turned in the north-south direction, the origin of the phases p may be the south and for an aircraft located to the north of a first radio beacon A, the spot of the oscillograph of Figure 4 will mark a radius directed vertically downwards (according to Figure l, i. e. with sinusoidal modulation of M). This same aircraft ying to the south-east, for instance, of a second radio beacon B, i. e. the bearing having rotated 135, for instance, in a clockwise direction, the oscillograph will mark a radius directed towards the northwest, and s0 forth. It is possible in this case to contemplate juxtaposing the image of the fluorescent screen on that of a geographical map directed in such a manner as to make the two north directions coincide, for instance by projecting the image of the screen on the map. It will then'jonly be necessary to shift the projection and the map relatively to one another, first sideways so as to bring the place A of the map on to the line OA, and then in the direction of said line until the place B of the map comes on to the line OB, in order to see directly opposite O the place over which the aircraft is flying. This manner of operating, although less direct, avoids the use of a transmitter on board the aircraft and, as hereinbefore stated, reduces the necessary band width and the modulation frequency F.

It will be observed that, in the case in which it is only desired to indicate the bearing, the cadence at which the various radio beacons on the ground are set in action may be considerably smaller than has been indicated. Thus, for instance, `'said radio beacons could be set in action only every tenth of a second during `a maximumlu.. a second. there will be received at the. output n,

time'of 10 milliseconds. The mark of the radii OA, OB, OC (Figure 1)v would then be seen on' the oscillograph ten times per second, which is still sufficient. This enables the modulation fre quency F to be further reduced.

'Another arrangement according to the linvention will now be described, which gives less complete indications, but which requires a simpler apparatus and consequently less expensive apparatus on board thel aircraft. It is possible, for

instance, to equip touring aircraft in this manportion 2l amplifying as a whole (optionally withV change of frequency) the waves M and )(2,01"y

M and M. Said waves are selected at 22 and are detected at 23. There are thusobtained, at the output terminals of the said detectors '23, voltages of the form cos Slt and cos (Qt-ga), fp' being the bearing required. One of these two voltages, for instance cos (Qt-qb), is fed to a manually operable dephasing circuit 24. At the Aoutput terminals of the dephasing device, said voltage s opposed to the second of the two voltages, and after optional amplification by the valve 25, the resulting voltage is fed to thetelephone 2t. For equal amplitudes of the two voltages, the resulting voltage is of the form:

Cos (Sit-e-l-) -cos Slt= phasing device 24. The resulting voltage therefore cancels out for 0= p, and increases linearlyv t with 0 for small values of (f1-e), thus giving great sensitivity to the measurement. For unl equal amplitudes, the zero is converted into a definite minimum owing to the increase of Sin on either side of the minimum.

One has in eect: A cos (Qt-p-l-o) -B cos slt= (A-B) cos Qt-qJ-j-o-i-B cos (Slt-qy-i-) -B cos (2t.

For c=9 the last terms on the right cancel each other.

There is also no indeniteness when@ variesI from 0 to 360.

graduated in bearings, said dial indicating the true bearing of the station involved.

It will nevertheless be noticed that this arrangement is incomplete when the aircraft receives the signals of several radio beacons, said I beacons transmitting successively, owing to they fact that the adjustment of the dephasing deorder to obviate this drawback, provision is made;

vice is not the same for the various stations.

for the signals received and already detected on one of the channels for obtaining the frequency il, Ito be detected again at 2 and for thevoltage ,thus obtained to synchronize an impulse generator 28 ensuring the operation of the valve 25. l

In fact, in each example chosen, according to which the radio beacons transmits successively every tenth ofka second during a hundredth of 0 designating the advance introduced in the de- The operating dial of the dephasing member 24 may therefore be directly' s' Passa-ec? "terminals of v21, if Asevered radio beacousa're re- 4lceivedl Yone 'after I'the other, "successive signals of =moreor less great amplitude according to whether the radio beacons Yare lmore or less distant, the

pulses btainedfro'm I27. It follows that'the telephone will only be connected to asingle predev"te'rrnined radio beacon.

It is always possible `to arrangevfo'r the generator n.".8 only tope-synchronised with'the trans- "rnitter producingV the "strongest impulses, thus only permitting the bearing of the strongest sta- `jtion to be taken; itis also possible to varrange Vfor 'j the generator Z8 tofbesynchronised with any station.v This result will-preciselybe obtained if the factual frequency Aof the generator '-28 'differs little from-thatof the'trans'mission of the radio beacons; thegenerator 28 will be synchronised "with anyone ofthe radio beacon transmissions, according Vto the instant which has been chosen to 'set it in operation.

In the variants previously'described, as thel fthree waves transmitted "M, X2, 'k3 are -very close together and'have to be selected by filtering, it is 'generally Vnecessary for the receiver to be of the Asu'perheterodyne type, the heterodyne being itself piloted by a quartz crystal of which the frequency Vvis' multiplied.

FAccording Vto another object of the invention,

the Aairborne receiver is simplifiedby causing the radio beacons to transmit directly, in addition to the above mentioned waves, a pure `continuous `wave on a frequency equal to that of the heterodyne. Thiswave, which is obtained from 'a quartz oscillator, may also be transmitted bythe aerial I of the system of f'aerials. The receiverwill in this case be identical 'to that ofFigure 4, save as regards the inputportion which will no longer include a frequency changer, the various intermediate frequencies being obtained direct by interference in the first detector, between the three vgrouped waves and the wave of the heterodyne frequency, which wave is itself transmitted by the ground radio beacon.

, 4 According to another object of the invention, "the, transmitter is furthermoreV simplified, and

Yalso the receiver, by eliminating the transmission 4on )e of the radiobeacons and the corresponding channel of the receiver. In this case, therefore, a group of waves will finally-be transmitted which" produces, l'at a distance, a'complex field of the form: 1

t'ofact asalieterodyne :atthe receiving end. It will be 4fobserv'ed that such a 'transmission `may 'cycle of the amplitude being repeated every'tenth of 'a second. If,there`for`e, tlfe impulse generator *of phase.

vby the resistance 4| and the detector d2.

ray oscillograph provided with magnetic deflection for instance, which may furthermore have a conical electrode in order to obtain radial de- `flectic'n electrostatically.

The receiver, which is fed by an aerial 3l (Figvu're'8), feeds the'block 32 comprising a very high 'frequency amplier followed by a single detector. {Ihe intermediate frequencies at the output of said Vdetector are then amplified, selected and separately'detected in the blocks 33 and 34, which are consequently amplifiers which are each tuned 'to vone of the two intermediate pulsations Q1 and At the output of these blocks are again present the voltages cos 21r Ft and cos (21T Ft-lp), of which it is necessary to measure the difference For this purpose, the block 33 feeds an amplifying valve 35 which can also act as a limiter owing to the high resistance R inserted in its grid circuit. Said valve feeds a group'of two circuits which are tuned to the frequency F and are magnetically coupled. The inductances '36V and 31 are formed by the magnetic deflection orthogonal'deflecting coils of the oscillograph. As is well known, a rotating field is thus produced, so that the lspot of the oscillograph describes a circular path at the frequency F. The diameter of the circle is limited by the limitation introduced by the valve 35.

V Similarly, the block 34 feeds the limiting valve 38 which is so biassed by means of the battery 39' that the flow of anode current is just cut off. The anode circuit of said valve contains a very rhigh frequency transformer 4S) which is damped The operation, which is moreover well known, of this arrangement, is as follows:

So long as the instantaneous alternating voltbe considered as `a`=tra'nsnission`which is'r'nodu-f'- Vand "and inwhich'the upper side band has been suppressed. The receiver modified according to the fore- Y"gifting Principle V`willvnow tbe"described Said vre- {qe'iver (Figure s) is Qmymtenaedpto give vune bearing arl-dto' 'operateinfrelationwth `a 'cathode the battery 39 Vand keeps the grid negative, the

valve 38 is blocked. When the alternating voltage changes sign by passing through zero, the anode Acurrent begins to flow through the valve 38 and quickly reaches saturation point. The circuit comprising 4U, 4l, 42 is then energised by shock, and 'sets up a short voltage impulse of which the sign is such that the detector 42, as it is shown connected, remains inoperative (negative directiontowards the anode). As known, the resistance 4| is'of such a value that it brings the cir- 'cuit near the point of critical aperiodicity, so that there is only a peak of voltage.

When the alternating voltage again becomes zero after a half-cycle, the voltage peak of opposite polarity is prevented from passing by the presence of the detector 42. A short voltage peak is thus obtained at each cycle of alternating current, said peak moreover coinciding with the instant when the alternating voltage passes through zero.

According tothe characteristic of the invention, this brief impulse, which can be obtained from the secondary terminals of the transformer 40, is used to contro-l the conical electrode of radial denection of the oscillograph, if said oscillograph'is provided with one, or else to illuminate the spot ofthe oscillograph by acting on the Wehnelt cathode. In the first case, a radius `directed along the bearings is obtained, and in the second a luminous point on the circle of which the other points are dark, said point bein'glikewise directed along the required bearing.

If the aircraft is flying over a region located 'in the zone of range of several radio beacons, theisame operatingsuccessively as hereinbefore mentioned, thesimultaneous bearing of all Vthese radio beacons is obtained, in the above explained form. on tbe oscillograph.

It may be more advantageous, in particular in' the case in which it is desired not to complicate the airborne installation with an oscillograph (case of Figure '7), to make the radio beacons which are in the saine region operate on adjacent but different wavelengths; there will be, for in- 4-stance, according to the arrangement of Figure The intermediate.v

2, nine adjacent wavelengths. pulsations Sii, Q2 and also the frequency F, will be the same for all the radio beacons. The difculties of synchronisation on the ground-will thus be eliminated, and only one call sign per region will be required.

The receiver of Figure 8 should in this case be completed by a tuning device on the high frequency portion 32 of the receiver. This device may, for instance, comprise a contact arm rotating quickly over studs, or a condenser of which the capacity can be varied in jumps and which is driven sujiiciently fast for each of the nine frequencies to be explored several times per second. The image seen on the oscillograph is thus not changed, but it is possible, lif the rotatingmember is stopped ori a predetermined tuning, to identify a radio beacon of a region by its wavelength, since there will only be on the screen the radio beacon corresponding to this wavelength.

Although this method of operation slightly complicates the receiver previously described, it

, simplifies on the other hand the receiver of Figure 7 (which relates to a Zero method), since the elements 2'! and 28 are eliminated from` the receiver, which elements were intended to isolate the reception of the radio beacon, on which it was desired to make the zero measurement, from the other radio beacons. It is, in fact, only necessary for there to be provided on said receiver a tuning adiustment to any of the nine frequencies considered. v

I claim:

1. In a system for the guidance of mobile craft, a plurality of similar radio beacons located each at a pretermined geographic location, means for controlling said plurality of beacons to emit periodic signals in a predetermined relative order, each of said beacons comprising a source for transmitting signals comprising a first carrier,

, said first carrier being amplitude modulated with a rst modulating wave, the phase of said iirst modulating wave having a constant Value at a fixed range from said source for all bearings from said source, each of said beacons further comprising means for transmitting two further carriers, said further carriers being each amplitude modulated in predetermined relative phase with a further modulating wave, the frequencies of said further modulating waves being equal to the frequency of said rst modulating wave, the phases of said further modulating waves varying with bearing about said source at a fixed range therefrom, an omni-directional antenna located on said mobile craft, means coupled with said antenna for receiving said carriers and for detecting said modulating waves transmitted by at least one of said radio beacons,'means for transmitting pulses from said mobile craft to said one of said radio beacons simultaneously with receipt of transmissions from said one of said radio beacons, means for returning to said mobile craft ocho pulses from said one of said radio beacons in response to transmission of said pulses to said one of said radio beacons, means aboard said aircraft for receiving and detecting said echo y pulses, means foramplifying said modulations of said further modulated carriers, means for conradio beacons.

2. The combination in accordance with claim 1, wherein said means for indicating comprises a cathode ray tube indicator having a cathode ray beam and a Screen for providing an image in response to impact by said cathode ray beam, means responsive to said modulations of said further modulated carriers for determining the angular position of said beam with respect to said screen, and means responsive to the gain of said means for amplifying for determining the radial position of said beam with respect to said screen.

3. In a system of radio navigation for mobile craft, a plurality of similar radio beacons, means for causing said radio beacons to transmit periodically in time succession at a rate of at least ten times per second at each radio beacon three signals each modulated with a modulating wave at the same frequency, a first of said three signals comprising a carrier wave and two side bands, the phase of said modulating Wave comprised in said first of said three signals having equal phase omni-directionally from its source, the modulating waves comprised in the remaining two signals having phases Variable equally and oppositely with azimuthal angle from their sources, an omni-directional antenna mounted on said mobile craft, means coupled with said omnidirectional antenna for amplifying and demodulating each group of three signals deriving from each of said radio beacons in succession for deriving from each of said groups a voltage having the form -B cos Slt and two further voltages having the forms respectively A cos (QH-qv) (-Qt) and -A cos (Qt-o) (-Slt), Q being the modulation frequency, and p the variable phase of the modulation, A and B being constants, a cathode ray tube indicator comprising means for generating an electron beam, means for deflecting said electron beam through said angle q1 in response to said further voltages, means for emitting pulses periodically from said mobile craft at times coinciding with reception of signals from at least one of said radio beacons, means for repeating said pulses to said mobilecraft from said at least one of said radio beacons, means at said mobile craft for receiving said repeated pulses, means at said mobile craft for amplifying said modulations with a gain which is a function of the time interval separating transmission and reception of said pulses aboard said mobile craft, and means for de- Y termining the amplitude of deflection of said elecprising three waves of slightly different wave length, each modulated in amplitude at the same frequency n, each of said radio beacons comprisreasons? 'i1l3 ingapentral vertical antenna located on'theve'r- *tical'axis'ofa squarevbased-prism of 'which vthe "four verticalsidesfare-constituted of four an- ''tennas for rproviding4 directional' patterns'to the 'North, South, East, and West'of-said central ver- 'ticalantenna, the distancesfbetween said antenbeing :small relative tothe wavelengths of A*said transmissions, `said "central verticalA antenna emitting a first Wave comprising a carrier and two side bands such that the upper side band when combined with the upper side band of the Waves emitted by said four antennas provides a resultant radiation pattern rotating at the angular velocity and S2, and such that the lower side band when combined with the lower side bands of the waves emitted by said four antennas pro vides a resultant rotational pattern of radiation rotating at the angular velocity Q. means aboard said aircraft for receiving and detecting said three waves, said last named means comprising an omni-directional antenna, an amplifier coupled with said antenna and having an output circuit, three filters connected with said output circuit for separating said omni-directional carrier from said side bands and said side bands from each other, each of said lters having an output circuit, a detector connected with each of said last named output circuits, two limiter stages connected at the output circuits of said filters for separating said side bands from each other, a cathode ray oscilloscope having an intensity control grid, means for connecting said intensity control grid to the output circuit of said filter circuit for separating said carrier from said side bands, f

two pairs of deection electrodes for said cathode ray tube indicator, means for connecting said limiter stages to said two pairs of deiiection electrodes to deflect said cathode ray beam angularly across said screen in accordance with the azimuthal bearing of said mobile craft from said at least one radio beacon, an airborne pulse transmitter having a pulse repetition rate different from the rate of transmissions from said at least onebeacon, or from an integral multiple of said rate, a time base voltage generator for generating `a time base voltage, means for applying said time base voltage to said limiters to control the limiting amplitude thereof, means for applying said time base voltage to said amplifier for controlling the gain thereof, means for eecting re-transmission from said central vertical antenna of each of said radio beacons to said mobile craft of said pulses transmitted by said pulse transmitter, and means aboard said aircraft responsive to said repeated pulses for initiating a visible indication on said cathode ray oscilloscope.

5. In a system of radio navigation for mobile craft, a plurality of similar fixed radio beacons for emitting signals periodically in a predetermined relative order, each of said signals comprising two Waves modulated in amplitude at the same frequency, each of said waves comprising a carrier and two side bands, the first of said waves having equal phase omni-directionally at any fixed distance from its source, the other of said waves having a phase variable with azimuthal bearing from said source at any fixed distance from said source, an omni-directional antenna on said mobile craft, means coupled with said antenna for amplifying, separating and detecting said two waves to provide two detected outputs, a phase shifting means, means for connecting of said means for demodulating for v-phaseshifte said phase fsliitingmeansf'in'cas'cade with one 'outputs Esaid .variable gain amplier lcomprising -a vacuum itu-beA having -a .gain controb grid, vand means for connecting the other of said leads to said gain control grid to control the gain of said gain control amplifier.

6. The combination in accordance ywith claim 5 wherein is further provided a pulse transmitter having an input circuit and an output circuit, means for connecting said output circuit between ground and one of said output leads of said phase shifting means, means for pulsing said pulse transmitter at the periodicity of one of said radio beacons, a low frequency detector having an input circuit and an output circuit, means connecting the input circuit of said detector to receive said one of said detected outputs, and means-for connecting said output circuit of said low frequency detector to the input circuit of said pulse transmitter.

7. In a system of radio navigation for aircraft, a plurality of radio beacons each located at a nxed geographic location, said radio beacons comprising means for transmitting on the same carrier frequency from each of said radio beacons in succession a radiation pattern comprising a component variable azimuthally from the transmitting radio beacon and a further component in variable azimuthally with respect to the transmitting radio beacon, means aboard said aircraft for deriving signals from said radiation patterns, said signals as received having magnitudes representative of the azimuthal bearings of said aircraft with respect to said radio beacons, means aboard said aircraft for selecting signals deriving from one of said radio beacons to the exclusion of the remainder of said radio beacons, and means responsive to said selected signals for creating an indication of the bearing of said aircraft with respect to said one of said radio beacons.

8. In a system of radio navigation for aircraft a radio beacon for transmitting into space a radiation pattern comprising a first carrier at a first radio frequency modulated in amplitude at a first modulation frequency, said modulation frequency having equal phase in all directions azimuthally from said radio beacons, said radiation pattern further comprising a second and a third radio frequency carrier at second and third radio frequencies respectively, said second and third carriers being modulated by relatively phase displaced modulation frequencies identical with said HENRI CHIREIX. i

(References on following page) REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,252,699 Byrne Aug. 19, 1941 2,253,958 Luck Aug. 26, 1941 2,313,048 Byrne Mar. 9, 1943 Number Delorane Apr, 26, 1949 

